Recovery of metal from coated metal foils



Aug. 2, 1932. R. B. DERR mscovmw OF ME TAL FROM COATED METAL FOILSOriginal Filed April 9, 1931 3 Sheets-Sheet l INVENTOR 24:0- A; MW.

Aug. 2, 1932. R. B. DERR 1,869,844

RECOVERY OF METAL FROM COATED METAL FOILS Original Filed April 9, 1931 3Sheets-Sheet 2 m In" INVENTOR k m. L H

Aug. 2, 1932. B. DERR RECOVERY OF METAL FROM COATED METAL FOILS OriginalFiled April 9, 1931 5 Sheets-Sheet 3 m m w M Mn m m m m m 1 xY 0 O E 6%7 QN New QM $1 R N N w N .7 wm

INVENTOR 7/: A aRIEI Patented, Aug. 2, 1932 UNITED STATES PATENT OFFICERALPH B. DERR, OF OAKMONT, PENNSYLVANIA, ASSIGNOR T0 ALUMINUM COMPANY OFAMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYL- VANIARECOVERY OF METAL FROM COATED METAL FOILS Original application filedApril 9, 1931, Serial No. 528,745. Divided and this application filedDecember 17, 1931. Serial No'. 581,780.

This invention relates to the recovery of metals from coated metalfoils, and particularly to the recovery of metallic aluminum ifiroinpaper-backed or lacquered aluminum This application is a divisional ofmy 00- pending application, Serial No. 528,745, filed April 9, 1931.

A large proportion of the metal foils now produced is prepared for useby being coated or backed with nonmetallic materials. For example, muchfoil is backed with paper attached to the foil by an adhesive. The papermay be untreated, or it may be waxed, in which case the wax may act asan adhesive. The foils may be coated on one or both sides with othermaterials also, such as Wax, lacquer or varn1sh. Large amounts of f01lscrap coated with such nonmetallic materials result annually fromtrimming and similar manufacturing operations.

Attempts to recover the foils from such scrap by washing the paper andother nonmetallic material from these coated foils, have beenunsuccessful, because complete and satisfactory separation could not beeffected. These coating materials are largely combus tible, and attemptshave been made also to burn the paper and other combustible matter fromthe foil. This procedure as practiced prior to this invention also hasbeen quite unsatisfactory, largely because considerable amounts ofcarbonaceous matter remained with the foil, and because the re sidualmetal was burned during treatment. Prior to my invention there has beenavailable no practical and economical means for reclaiming the foil insuch scrap. Its disposition, therefore, has been a serious prob- A majorobject of this invention is to provide means for recovering the metalfrom backed or coated foils, which removes all volatile and carbonaceousmatter from the foil, avoids burning of the metal, is simple,economical, may be readily and positively controlled, provides a productthat is clean, bright, and of uniform quality, and is especially adaptedfor the reclamation of aluminum foil from coated aluminum foil.

F i 2; Fig. 2 a sectional View through a unit taken on line IIII, Fig. 1showing a fragmentof the foil basket; Fi 3 a section- 211 view taken online III-111 Fig. 4 a schematic plan view of a gas circulating systemadapted to the three-unit system of Fig. 1.

The invention is predicated upon my'discovery that paper, adhesive, wax,lacquers and the like non-metallic components of Fig. 1; and x backed orcoated foils may be removed.

readily and economically, and without burning the foil, by firstdistilling volatile combustible matter from the backed foil by heatingit in a non-oxidizing atmosphere, and then burning ofi' residualcarbonaceous matter in an oxidizing atmosphere controlled in a mannerpresently to be described. The foil remains in a clean bright anddirectly utilizable condition.

The process, therefore, comprises two steps, or stages. In the firststage any wax andother volatile matter is distilled ofl, togetherwithproducts of destructive distillation of the paper, adhesive, lacquers,wax and the like. My tests have shown that there then remains a residueof carbonaceous matter, which is burned off in the second stage undercontrolled oxidizing conditions. All such coating materials-are, forbrevity of reference, referred to herein as volatile matter. Also,whether backed with paper, or covered with lacquer, wax, or othernonmetallic materials, the foils contemplated will be referred tohereinafter as coated foils.

In heating such backed foil in the presence of air the combustibles, forinstance wax and paper, will ignite, causing burning of the foil as aresult of the rapid and violent combustion. This makes the reclaimedfoil unsatisfactory for further use. In contrast thereto the benefits ofthe process provided by this invention are due in part to removal of thevolatile matter by heating the backed foil in a closed container fromwhich oxidizing gases are excluded. By thus heating in a non-oxidizingatmosphere distillation of the volatile matteris effected without itscombustion in contact with the metal.

The invention is predicated further upon my discovery that residualcarbonaceous matter remaining after the first step may be removedwithout damage to the metal by continuing the heating while admittingair, or other oxidizing or oxygen-containing gas,

so as to maintain an atmosphere of low oxygen content in contact withthe metal. In other words, the oxidizing atmosphere in this stage iscontrolled to burn off the carbona; ceous matter without burning thealuminum. In this stage the rate of gas supply is dependent in part uponthe oxygen content of the gas supplied to the container, and upon thetemperatures of the gas and metal.

The invention is applicable to the treatment of coated metal foilsgenerally for separation of the metal from the non-metallic coating andbacking materials. For purposes of description, and not by way oflimitation, it will be described with particular reference to thereclamation of metallic aluminum from paper backed aluminum foil, forwhich use the invention is especially adapted.

In the treatment of aluminum foil both steps are conducted preferably attemperatures from about 800 to 1000F. This range of temperature issuited to most coated aluminum foils and appears .to provide theshortest treatment times consistent with good results. Lower or highertemperatures than these may, however, be found desirable under certainconditions, and for foils other than aluminum. Thetemperature should notexceed the melting point of the metal.

The oxidizing gas supplied in the second stage may be air, but my testshave shown that, in general, the rate of flow of pure air over the foilmust be relatively low. Relatively high rates of flow are desirable inorder to remove the heat from the foil more rapidly. Accordingly, it ispreferable to obtain the desired low oxygen atmosphere by mixing airwith an inert gas, as by using a flue gas of controlled oxygen content.Satisfactory results are had with a flue gas containing 5 to 8 per centof oxygen.

It is important that the atmosphere in the container during the firststage of the process be essentially non-oxidizing. No gas need beadmitted, but it may be found desirable to introduce a non-oxidizinggas, such as carbon dioxide, to assist in carrying the heat to the foilmass, and more rapidly to carry off the volatile matter. Generally, inoperating as described herein, about 85 to 90 per cent of thecombustible matter will be distilled off in the first stage.

The most satisfactory results are had by circulating the gas uniformlythrough the mass in the second stage. This is productive of uniformlyclean bright foil, and it aids heat control, and shortens the treatmenttime. ,Also, the gases passed to the retort may be, and preferably are,preheated, for instance to about the temperature of the foil undergoingtreatment.

My tests have shown also that it is desirable to pack the foil scrap inthe container, rather than inserting it loosely. Satisfactory resultsmay be had with foil packed to a density of 0.75 to 1.25 pounds percubic foot, the lower density being used with lighter foils.

Control of the process is accomplished by means of an apparatusembodying an externally heated gas-tight retort, in which the foil istreated, and which is provided with means for controlling the atmospherein contact with the foil during treatment. Regulation of the atmospherein the second stage is had most suitably by recirculation of gases fromcombustion of the carbonaceous matter in that stage.

The preferred embodiment of apparatus is shown in the accompanyingdrawings. Fig. 1 shows an apparatus embodying three units, eachcomprising a gas-tight retort 1 disposed within a combustion chamber 2built up in any suitable manner from refractory and insulating brick 3and 4.- respectively.

As shown well in Fig. 3 the retort comprises a rectangular base member'5and an upper hood member 6 supported in grooves formed therein in suchmanner as to form a substantially gas-tight seal. To this end base 5 isprovided with peripherally disposed upwardly extending flanges 8 and 8aspaced to form a groove 9 which receives the bottom of hood 6 and isfilled with a sealing medium, such as sand. The base is mounted on acourse of refractory brick 3a carried by pillars 7.

The hood is open at one end for charging,-

and this opening is closed by a doofIO. In order to exclude air from theretort during distillation, door 10 is forced by cam levers 11 againstasbestos rope packing 12 arranged in a groove in the door correspondingto the charging opening. vA gas-tight seal is thus formed. This door maybe mounted in any suitable manner, as for example by means of thecounterweighted mechanism shown.

The retort is fired externally by heat generated in the combustionchamber. In the apparatus shown burners 13 projecting into thecombustion chamber below the base of the retort provide the necessaryheat. These burners may use either gaseous fuel, or oil.

' basket 14 having a foraminous base, so that gas may be uniformlycirculated upwardly through the foil. Basket 14 is formed from sheetmetal sides and ends, suitably reinin the second stage of the process,that is in Y the burning off of carbonaceous matter in a controlledoxygen-containing atmosphere, these units will require a mixture of fluegas and air in controlled proportions. Valves 23 of these two units areturned to direct the forced, and its bottom suitably consists ofa/products of combustion into conduit "28, as

sheet 15 of expanded metal carried on transverse supporting-members 16.About the periphery of-the bottom of the basket is connected aZ-bar 17whose depending leg extends into a groove 18 formed peripherally of theretort base by a flange 19 disposed inwardly from flange 8a. This grooveis also filled with a sealing medium, such as sand. This constructiondirects gas supplied below the basket upwardly through its contents in amanner productive of the best results.

The atmosphere in the retort is controlled by gas supplied from amanifold system carried by the retort base below the basket. Theembodiment shown comprises headers 20 and 20a disposed longitudinally ofthe sides of the retort base and connected at one end to.

a gas supply line 21. The headers are connected by a parallel series oftransverse pipes 22 perforated along their under sides to effect properdistribution of the gas uniformly over the entire area defined by thebottom of the basket.

Volatile matter distilled from the foil, and

gaseous products of combustion formed in- The units just describedpermit 'of reclamation of foil in accordance with this'invention. Theseunits. may be usedsingly, or a number may be" built up into a combinedstructure, for example as shown in Fig. 1. The construction of theheating chamber or retort is such as to prevent any substantial leakageof .air into it, and thisis important in effecting the distillationstage. Control of the atmosphere in the retort thus is easy.

During combustion of carbonaceous matter in the second stage of theprocess the flue gases contain carbon dioxide. In the preferred practicethese gases are. recirculated as a conveneient means of controlling the.

oxidation in the manner set forth.

Such recirculation may be had .by the pining layout shown in Fig. 4, forthe three unit apparatus shown in Fig. 1. The units areindicated by theletters A, B and C. The products of combustion or'distillatio'n, as t ecasemay be, pass from the retorts to val es 23. Assuming thatunits A andBare operating shown bythe arrows, Fig. 4. A portion of the This knowntypes, it being mounted in manifold ,29 and controlling a valve in theair inlet.

The mixture of flue gas'and air is passed by the blower to manifold 29.Valves 34: at each unit, control flow from the manifold to gas lines 21.Valves 34 in units A and- B are opened, and the gas mixture isdistributed through headers 20 and pipes22 to the retorts. J

v Unit C is being used in the first, or distillation stage. The wax andother com: bustible matter may be permitted to burn outside oftheretort. Preferably, however, the

volatile roducts are drawn off through branch 24 and passed to stackthrough flue 26." The wax may be'separated from these gases, if desired,by an appropriate condenser 35. During this stage valve 34 for unit Oisclosed. L

By the use of a furnace of suificient heat capacity, the chambers mightbe hot enough,

after the first stage of the treatment, to maintain suitabletemperatures throughout the second stage of the treatment, and to startdistillation in an immediately following treatment. Thus, bysuitabledesign of furnace and control of its continuous operation, the heatderived from the products of combustion may be so conserved that the supply of external heat becomes unnecessary once the furnace has been putinto operation.

Tests made with an apparatus similar to that described have shown thatpractically all aluminum foils maybe recovered satisfacftorily bypacking them to about the densities described in beds of from two. tothree feet deep, and heating to about 800to 1000 F. The

first stage usually requires about one and onehalf to two hours. Usingin the secondstage a mixtureof flue gas and air containing from about 5to 8% of oxygen, preheated to about 800 to 1000 F. and passed throughthe foil at a rate varying between about 0.25 and 0.6

cubic foot per square foot of surface per minute, this step generallyrequires about four to six hours.

Backed foil treated in the manner just described is' entirely freed fromthe backing matter, and it is of bright, clean and uniform quality. Attimes the foil may contain small amounts of a loose flufiy ash. Such ashmay be readily separated from the foil by screening or aerating.

According to the provisions of the patent statutes, I have, explainedthe principle and mode of operation of'my invention and have illustratedand described What I now con; siderto represent its best embodiment.However, I desire to have it understood that, within the scope of theappended claims, the inyention may be practiced otherwise than asexternally fired gas-tight retort provided with a charging door and agas take-ofi', a plurality of perforated pipesdisposed with- L in saidretort adjacent its bottom and connected to a source of gas forcontrolling the atmosphere in the retort, and a foil-containing baskethaving a foraminous bottom disposed over said pipes for circulation ofsaid gas upwardly through foil disposed in the basket.

.heatin grooves formed between upwardly extending flanges, a hood havingits lower edges sup orted in said outer grooves, a foil-receiving askethaving a "foraminous bottom supported peripherally in said inner groove,sealing medium in said grooves, and a plu-' rality of parallelperforated pipes disposed beneath said foraminous bottom and con nectedto a source of gas for controlling the atmosphere in the retort.

6., An apparatus for reclaiming aluminum foil from paper-backed foilcomprising a chamber and a retort mounted therein, sai retort comprisinga base provided in its upper surface with outer and inner parallelgrooves, a hood provided with a oharging door and supported peripherallyin said outer groove, a foil-recei'vin basket insertable through saiddoor, said basket having a foraminous bottom and being supportedperipherally in said inner groove, a sealing medium in said grooves,pipes disposed beneath said foraminous bottom for supplying a controlledatmosphere to foil in the basket, and a header connected to said pipes.

7. An apparatus according to claim 4, and means for recirculating gasesfrom the retort through said pipes.

In testimony whereof 1 hereto aflix my signature.

RALPH B. DER-R.

3. An apparatus for reclaiming aluminum foil from paper-backed foilcomprising a heating chamber, a gas-tight retort disposed therein andcomprising a lower base portion having a peripherally disposed sealinggroove containing a sealing medium, and an upper hood portion supportedby said base a in said groove,-a foil-receiving basket insertablethrough said door and having a foraminous bottom disposed -in saidretort, and means for uniformly supplying a desired gas to the bottom ofsaid basket for,

circulation through foil disposed therein.

4. .An apparatus for reclaiming aluminum foil from paper-backed foilcomprising an externally fired gas-tight retort provided with a chargingdoor and a gas take-off, a plurality of perforated pipes disposed withinsaid retort adjacent its base and connected to. a source of gas forcontrolling the atmosphere in the retort, a foil-receiving basketdisposedin said retort, said basket having a foraminous base and beingdisposed over said pipes for positive circulation of said ga through itscontained foil.

5. A retort for reclaiming aluminum foil from paper-backed foilcomprising a base provided in its upper surface with parallel out??? dinner peripherally disposed

